1. Field of the Invention
The present invention generally relates to a display panel driving device.
2. Description of the Related Art
One type of display panels is an active matrix type display panel that includes a plurality of address electrodes and a plurality of data electrodes. The address electrodes and data electrodes intersect with each other perpendicularly such that a plurality of display elements are sandwiched (defined) between the address electrodes and data electrodes. Organic electroluminescence (hereafter simply referred to as “organic EL”) light-emitting elements are used as the display elements. Such display panel is disclosed in, for example, Japanese Patent Application No. 2002-93856. The entire disclosure of Japanese Patent Application No. 2002-93856 is incorporated herein by reference. The structure of this display panel is schematically shown in FIG. 1 of the attached drawings.
In FIG. 1, a display panel 10 includes a plurality of display elements arranged in a matrix form. The display elements include TFT elements and organic EL light-emitting elements. According to the VGA (Video Graphics Adapter) standard which is an international standard for display panels, the display elements of the display panel 10 are arranged in, for example, 640 (x RGB) columns by 480 rows of dots.
The X transfer circuit 20 which is a peripheral circuit of the display panel 10 supplies image data signals (referred to as “data signals”) to each of the display element groups arranged in the 640 (x RGB) columns. That is, 640 parallel data electrodes extend from the X transfer circuit 20, for each of the RGB display elements, in the X-axis direction of the display panel 10.
The Y transfer circuit 30 selects, with prescribed timing, one of the display element groups in the 480 rows, and supplies an address signal, which is a selection signal, to the selected row of display elements (selected display element group). The 480 parallel address electrodes extend from the Y transfer circuit 30 in the Y-axis direction of the display panel 10.
Hereafter, in this specification the X transfer circuit 20 and Y transfer circuit 30 which are peripheral circuits of the display panel 10 are jointly referred to as the driving device of the display panel 10.
Conventionally, the driving device mainly includes shift registers and other active circuits. For example, the X transfer circuit 20 uses a 640-stage shift register to sequentially shift X transfer pulses contained in the X transfer signal shown in FIG. 1, and relies upon the shifted pulses to sample-hold analog signals for the RGB display elements so as to generate the above-mentioned data signals. The Y transfer circuit 30 uses a 480-stage shift register to sequentially shift the Y transfer pulses contained in the Y transfer signal shown in FIG. 1, to generate the above-mentioned address signals.
In order to configure a sequential logic circuit such as a shift register and a sample-hold circuit, transistors with both polarities, P-channel and N-channel, are required. Consequently, amorphous silicon and organic semiconductors, from which only unipolar transistors and diodes can be fabricated, cannot be used as the semiconductor material for the driving device of the display panel 10. Therefore, low-temperature polysilicon semiconductor material, which is costly and involves complicated production processes, is primarily used.